For a typical scanning force microscope such as the atomic force microscope, a micromachined tip is scanned across a surface which results in the cantilever attached to the tip being deflected. Typically, the cantilever is controlled in the direction normal to the surface being scanned by an actuator such as a piezoelectric tube or a MEMS actuator. The deflection is typically detected by illuminating the cantilever using a laser beam. While it is possible to measure the deflection and use that as a position signal, large deflections may damage the tip and the surface being scanned. By ensuring that the deflection is close to some nominal point by moving either the cantilever or the surface being scanned, any potential damage is reduced. Hence, an additional signal besides the cantilever deflection is typically needed to provide an estimate for surface height.